The anticipated end of Moore's law scaling in microelectronics has stimulated researchers to explore other alternatives i.e. to render the individual components to be multifunctional. One of the promising field in which the researchers have focused in order to explore the multifunctionality of the materials is Magnetoelectric (ME) multiferroics.
(ME) multiferroics are materials which possess simultaneously ferroelectric (FE) and ferromagnetic (FM) properties in the same phase and have coupling between them, that is, the switching of magnetization by electric field or polarization by magnetic field; have had a tremendous research interest due to a number of potential multifunctional applications in modern technologies, like sensor applications and random access memory devices. These ME materials have all the potential applications of their parent FE and FM materials; in addition to having a bifunctional property not available in systems with a single order parameter.
The ideal ME multiferroic materials for device application would be a single phase material with high FE and FM properties, low leakage current, and a strong coupling between FE and FM properties which allow the control of the magnetic properties with electric field and vice-versa, at room temperature. There are several families of the single phase ME multiferroic materials such as i) perovskite oxide structure family (Bismuth compounds, Relaxor, rare earth (RE) manganites (REMnO3), Mixed Perovskite solid solution); ii) Other oxides (REMn2O5 family); iii) Non oxides (phosphates, boracites, fluoride family, spinel chalcogenides, and delafossites). Most of the compounds listed above have drawbacks: i) they are multiferroic at low temperature; ii) they have very low ferroelectric and/or ferromagnetic response; and iii) low value of magnetoelectric coupling constant for practical applications. In case of multiferroic terbium manganites TbMnO3 or TbMn2O3, the inconvenience for practical applications is their weak ferroelectric properties at very low temperature (<40 K). It is two orders of magnitude smaller (<0.1 μC/cm2) than a typical ferroelectric polarization (1-100 μC/cm2).
However, in perovskite oxide structure family, one of the promising Bi compound is BiFeO3 (BFO), which has multiferroic behavior at room temperature, with a remanent polarization ˜50-60 μC/cm2, but it exhibits a weak ferromagnetism (1μB per unit cell), which makes the cross coupling among these ferroic parameters very weak and also poorly understood. Additional problems with BFO are high leakage current, a tendency to fatigue, and thermal decomposition near the coercive field. In case of relaxors such as Pb(Fe2/3W1/3)O3 (PFW) and Pb(Fe0.5Ta0.5)O3 (PFT), they show high temperature multiferroic behavior. One of the reason why single phase oxide multiferroic materials have been reported in small numbers is due to the contra-indication between the conventional mechanism in ferroelectric oxides that requires empty d-orbitals and formation of magnetic moments which results from partially filled d-orbitals. In order to overcome the intrinsic limitations to obtain high magnetoelectric coupling, the efforts of scientists are aimed at synthesizing new single phase material that can produce electric switching of magnetization and magnetic switching of polarization at room temperature with electrical requirements (low leakage current, low fatigue, low loss) that allow its use for practical applications. In this sense, perovskite solid solution method, opens the door to the possibility of finding a desired single phase ME multiferroic material.